A sputtering apparatus which deposits a thin film on a substrate includes an evacuated vacuum vessel, a target holder which holds a vapor deposition source called a target made of a material to be deposited on the substrate in the vacuum vessel, and a substrate holder which supports the substrate in the vacuum vessel. In a process of depositing a thin film on the substrate, the sputtering apparatus introduces a gas such as Ar into the vacuum vessel, and applies a high voltage to the target, thereby generating a plasma. A phenomenon in which charged particles in the discharge plasma sputter the target is exploited to allow the target material to adhere onto the substrate supported by the substrate holder.
When positive ions in a plasma strike a target material with a negative potential, atoms and molecules in the target material are ejected from the target material. These atoms and molecules are commonly called sputtering particles. The sputtering particles adhere onto the substrate to form a film containing the target material on it. The sputtering apparatus typically includes a freely openable/closable shield plate called a shutter, which is inserted between the target material and the substrate.
The shutter is used mainly for the following three purposes. First, the shutter is used to prevent sputtering particles from scattering until the discharge stabilizes. More specifically, the sputtering apparatus does not generate a plasma simultaneously with high-voltage application but normally encounters the following phenomena. For example, a plasma is generated with a delay of about 0.1 sec after voltage application, is not generated even after voltage application, or is generated but is unstable immediately after the start of discharge. These phenomena make it impossible to deposit a film with a stable thickness and quality. To circumvent this problem, the shutter is used for so-called pre-sputtering, in which discharge starts while the shutter is closed, and the shutter is opened after the discharge stabilizes so that sputtering particles are deposited on the substrate.
Second, the shutter is used to perform conditioning. The conditioning means discharge which does not aim at depositing a film on the substrate but aims at stabilizing the deposition characteristics.
For example, before the start of continuous deposition to yield a product, discharge is performed under the same conditions as continuous deposition conditions in order to stabilize the atmosphere in the vacuum vessel. Especially in a reactive sputtering method of introducing a reactive gas such as nitrogen or oxygen or a mixture of a reactive gas and Ar into the vacuum vessel to deposit a nitride or oxide of the target material on the substrate, it is important for stable deposition to keep the inner surface of the vacuum vessel in the same state as the state in which continuous deposition is performed.
However, sputtering particles adhere not only onto the inner surface of the vacuum vessel but also onto the substrate mounting surface of the substrate holder. To prevent this, discharge is performed after an inert gas and a reactive gas are introduced into the vacuum vessel while preventing a film from adhering onto the substrate mounting surface of the substrate holder by closing a shutter disposed in a vicinity of the substrate holder so as to shield the substrate mounting surface when viewed from the sputtering surface and so as not to shield the inner surface of the vacuum vessel. With this operation, a nitride or an oxide adheres onto the inner surface of the vacuum vessel. The quality of a thin film to be deposited can be stabilized by starting deposition on the substrate after a nitride or an oxide adheres onto the inner surface of the vacuum vessel in sufficient quantity in advance.
Conditioning is also often performed as discharge under conditions different from the production conditions in the process of continuous deposition to yield a product. This applies to a case in which, for example, a film with a strong stress is continuously deposited on the substrate by the reactive sputtering method, so a film adhering on, for example, a deposition shield in the vacuum vessel peels off and becomes a particle. To prevent this, a metal film is often periodically deposited using a nonreactive sputtering method. For example, conditioning of Ti deposition is periodically performed in continuous TiN deposition. When only TiN is continuously deposited, a TiN film adhering on, for example, the deposition shield in the vacuum vessel peels off. However, this phenomenon can be prevented by periodically performing conditioning of Ti deposition.
Third, the shutter is used to sputter a contaminated or oxidized target surface in advance to remove the contaminated or oxidized portion of the target before continuous deposition to yield a product. More specifically, a target is shaped by machining using, for example, a lathe in the final process of manufacturing the target. At this time, contaminants produced by a grinding tool adhere onto the target surface, or the target surface oxidizes during transportation of the target. This makes it necessary to sufficiently sputter the target surface before deposition to expose a clean target surface. In this case, the shutter is used for so-called target cleaning in which the target is sputtered while the shutter is closed so as to prevent contaminated or oxidized target particles from adhering onto the substrate mounting surface of the substrate holder.
Against a backdrop of the recent demand for an improvement in performance of devices, the following problem is posed. A target material which has adhered onto the lower surface of a semiconductor substrate in a sputtering process peels off or is carried to the subsequent processes and contaminates apparatuses in the subsequent processes, thus degrading the device performance. Note that contamination of other apparatuses through the medium of the lower surface of the substrate must be strictly controlled because it has a considerable adverse effect on the device performance even when the amount of adhesion of the target material onto the surface of the substrate holder in its portion where the substrate is placed is as very small as about, for example, 1×1011 atms/cm2.
This problem is encountered because there are gaps around the shutter even when the shutter is closed and they pass a small amount of sputtering particles. That is, sputtering particles adhere onto the substrate holder during conditioning or target cleaning. If the amount of adhesion is considerable, a film is deposited on the substrate holder. The deposited film not only contaminates the substrate upon adhering onto the lower surface of the substrate but also contaminates other manufacturing apparatuses as it is transported to the next process.
To circumvent the problem that sputtering particles land on the substrate mounting surface during target cleaning or pre-sputtering, PLT1, for example, discloses a technique of surrounding the target with a cylindrical cathode cover, and inserting a shutter into the opening in the cathode cover. This method is effective as a means for preventing sputtering particles from landing on the substrate mounting surface.
Also, PLT2 and PLT3 each disclose an apparatus including two shutters inserted between a substrate and a target or between the substrate and a vapor deposition source.